This invention relates generally to a light controller with occupancy sensor and more particularly to a light controller having an energy efficient, battery powered occupancy sensor.
As is well known, fluorescent lamps offer large energy savings as compared to incandescent lamps. For example, a 28 watt fluorescent lamp produces about the same amount of light as a 100 watt incandescent lamp. With the development of remote controlled fluorescent lamp ballasts, as described in U.S. Pat. Nos. 5,055,746, 5,068,576 and 5,107,184, the contents of which are incorporated herein by reference thereto, fluorescent lamps are now used in applications heretofore restricted to incandescent lamps.
Additional energy savings can be achieved through use of dimmable fluorescent lamp ballasts, that is, through the use of ballast control circuitry (hereinafter referred to as a light controller) for reducing the level of light produced by the fluorescent lamp. Reduction in the level of illumination is particularly applicable in lighting unoccupied areas.
The state of occupancy is typically determined through the use of motion sensors, that is, sensors for detecting the movement of an occupant. These detectors, although having a relatively wide field of view, are nevertheless dependent on their position relative to the occupant. Determining the state of occupancy within an area can be especially difficult when the sensor is not positioned near a relatively motionless occupant (e.g. when the occupant is seated).
A conventional occupancy sensor is generally mounted on a wall or ceiling of a room and integrally connected to the light controller at the time the room is built. The subsequent arrangement of furniture within or shape of the room can block or otherwise limit the field of view of the sensor. It can therefore be difficult for the sensor to determine with a high degree of reliability the state of occupancy within the room.
It is therefore desirable to provide an occupancy sensor independent of (i.e. not physically connected to) the lamp controller. In order to optimize placement of the sensor within the room, the sensor should be battery powered, that is, independent of connection to a utility power line. The sensor also should be operable for extended periods of time (i.e. well over a year) and in combination with a light controller provide automatic light dimming control for an unoccupied area.